A composite desulfurizing agent for absorbing sulfur dioxide and its preparation process

Abstract

This invention relates to the field of desulfurizing agents, and discloses a composite desulfurizing agent for absorbing sulfur dioxide and its preparation process. The desulfurizing agent is prepared by reacting ethanolamine, ethylene oxide, sodium hydroxide, zirconium-modified silica-alumina molecular sieve, and 1,4-bis(3-methylimidazolyl)butane dibromide. This invention uses a dual-template agent to synthesize the zirconium-modified silica-alumina molecular sieve catalyst; a premixed amine solution is contacted with the loaded molecular sieve, and ethylene oxide is introduced under a certain temperature and pressure to carry out a catalytic polymerization reaction, followed by filtration to obtain the final product. This invention utilizes the Lewis acid sites and hierarchical pore structure of the zirconium-modified molecular sieve to improve the selectivity and mass transfer kinetics of the polymerization reaction; the introduced ionic liquid constructs a dense supramolecular hydrogen bond network through dual cation centers, effectively inhibiting oxidative degradation and component volatilization, and utilizes flexible chains to reduce high-temperature regeneration viscosity. The resulting desulfurizing agent has advantages such as high saturated sulfur capacity, fast adsorption rate, good cycle stability, and high regeneration efficiency.

Description

Technical Field

[0001] This invention relates to the field of desulfurizing agent technology, specifically to a composite desulfurizing agent for absorbing sulfur dioxide and its preparation process. Background Technology

[0002] Sulfur dioxide is a common major pollutant in industrial waste gas and natural gas. Currently, the mainstream industrial desulfurization process uses alkanolamine solutions as absorbents. Although the alkanolamine method is technically mature and has a fast absorption rate, its essence is based on a strong chemical reaction, which leads to three major drawbacks that are difficult to overcome: First, the strong chemical bonding requires a huge amount of heat energy for desorption and regeneration, resulting in high operating costs; second, alkanolamines are extremely prone to oxidative degradation in oxygen-containing or high-temperature environments, generating thermally stable salts, leading to equipment corrosion and loss of effective components; third, small-molecule alkanolamines have high vapor pressures and are easily volatilized with the exhaust gas during the circulation process, causing secondary pollution.

[0003] To address these issues, the industry has attempted to introduce physical adsorption groups such as ether bonds through polymerization modification to construct a dual "physical-chemical" absorption system. However, existing synthesis processes mostly employ conventional catalysts and lack precise control over the polymerization reaction, resulting in a wide molecular weight distribution of the products. Excessively large molecular weights significantly increase the viscosity of the desulfurizing agent, severely increasing gas-liquid mass transfer resistance and slowing down absorption kinetics. Furthermore, traditional microporous molecular sieve catalysts, due to their narrow pores, struggle to diffuse large molecular products, easily leading to pore blockage. Therefore, developing a system with a multi-level pore structure capable of directional catalysis is crucial to solving the problem of limited mass transfer.

[0004] On the other hand, ionic liquids are considered ideal modifying additives due to their non-volatile nature and good thermal stability. However, traditional mononuclear ionic liquids have a low density of active sites per unit mass and high viscosity, resulting in less than ideal saturated sulfur capacity. Although simple physical mixing can improve the performance of desulfurizers to some extent, the lack of strong intermolecular interactions makes the active components prone to phase separation or loss during high-temperature regeneration or long-term gas purging, leading to poor cycle stability.

[0005] Therefore, there is an urgent need to develop a composite desulfurizer that combines high sulfur capacity, excellent antioxidant properties, and low regeneration energy consumption, and to solve the technical problems of poor reaction selectivity and easy loss of active components during its synthesis process. Summary of the Invention

[0006] (a) Technical problems to be solved: To address the shortcomings of existing technologies, this invention provides a composite desulfurizing agent for absorbing sulfur dioxide and its preparation process, solving the problems of easy loss of active components, poor antioxidant properties, and high regeneration energy consumption in composite desulfurizing agents.

[0007] (II) Technical Solution: In a first aspect, the present invention provides a composite desulfurizing agent for absorbing sulfur dioxide, wherein the composite desulfurizing agent for absorbing sulfur dioxide is prepared by reacting the following raw materials: 20-50 parts by weight of ethanolamine, 40-60 parts by weight of ethylene oxide, 2-5 parts by weight of sodium hydroxide, 1-3 parts by weight of zirconium-modified silica-alumina molecular sieve, and 0.5-2 parts by weight of 1,4-bis(3-methylimidazolyl)butane dibromide.

[0008] Furthermore, the preparation method of zirconium-modified silica-alumina molecular sieve is as follows: Step (1): Add boehmite, 80-85% phosphoric acid solution, and silica sol to the reaction vessel, stir and mix to form a gel.

[0009] Step (2): Add zirconium oxychloride solution as a metal source, hexadecyltrimethylammonium bromide as a mesoporous directing agent, and tetraethylammonium hydroxide as a microporous template agent to the gel. Mix well and add 15-25% ammonia solution to adjust the pH to 7-7.5 to obtain a mixture.

[0010] Step (3): Transfer the mixture into the reactor and hydrothermally crystallize it at 180-200℃ for 24-48 hours.

[0011] Step (4): The product is washed with deionized water until the filtrate is neutral, dried at 100-110℃ for 8-12h and calcined at 500-600℃ for 4-6h to obtain zirconium-modified silica-alumina molecular sieve.

[0012] Further, in step (1), the mass ratio of boehmite, phosphoric acid solution with a concentration of 80-85% and silica sol is 1:(2-2.5):(0.6-1).

[0013] Furthermore, in step (2), the concentration of the zirconium oxychloride solution is 5-15 wt%.

[0014] Furthermore, in step (2), the mass ratio of zirconium oxychloride solution to hexadecyltrimethylammonium bromide is (2-5):1; and the mass ratio of tetraethylammonium hydroxide to boehmite is (0.5-1.5):1.

[0015] Furthermore, the preparation method of 1,4-bis(3-methylimidazolyl)butane dibromide is as follows: 1-Methylimidazole and anhydrous ethanol were added to a reaction vessel equipped with a condenser and mixed thoroughly. 1,4-Dibromobutane was added dropwise, and the mixture was heated to 80-85°C and kept under reflux. The mixture was stirred for 20-24 hours. The product was cooled to room temperature, and ethyl acetate was added. The mixture was allowed to stand and separate into layers. The mixture was filtered, and the solid was washed five times with ethyl acetate and dried under vacuum to obtain 1,4-bis(3-methylimidazolyl)butane dibromosalt.

[0016] Furthermore, the mass ratio of 1-methylimidazole, anhydrous ethanol, and 1,4-dibromobutane is (8.5-9.5):(35-45):10.

[0017] Secondly, the present invention also provides a preparation process for a composite desulfurizing agent for absorbing sulfur dioxide, wherein the preparation process for the composite desulfurizing agent for absorbing sulfur dioxide is as follows: S1. Premixing and Activation: Mix ethanolamine, sodium hydroxide, and 1,4-bis(3-methylimidazolyl)butane dibromide evenly, heat to 50-60℃, and stir until the sodium hydroxide is completely dissolved to form a uniform and transparent modified amine solution.

[0018] S2. Loading of zirconium-modified silica-alumina phosphate molecular sieve: The zirconium-modified silica-alumina phosphate molecular sieve is loaded into the catalyst basket of the reactor.

[0019] S3. Polymerization reaction: Seal the reactor, replace the air with nitrogen, raise the temperature to 130-150℃, control the pressure at 0.5-2MPa, continuously pump in ethylene oxide, and after the pumping is completed, age at 100-120℃ for 1-2 hours.

[0020] S4. Post-processing: After the reaction is completed, the reaction solution is cooled to 40-60℃ and centrifuged and filtered to recover the zirconium-modified silicon aluminum phosphate molecular sieve. The filtrate is the composite desulfurizing agent.

[0021] (III) Beneficial technical effects: 1. This invention introduces zirconium-modified silica-alumina molecular sieve as a key catalyst during the synthesis process. The introduction of the transition metal zirconium provides abundant Lewis acidic sites to the system, enhancing the catalytic activity and regioselectivity of the ring-opening polymerization reaction of ethanolamine and ethylene oxide, ensuring that the product has a suitable molecular weight distribution and a large number of ether bond physical adsorption sites. Simultaneously, this invention employs a dual-template agent system composed of hexadecyltrimethylammonium bromide and tetraethylammonium hydroxide, effectively eliminating the diffusion resistance between macromolecular reactants and products, establishing a highly efficient mass transfer channel, and overcoming the pore blockage effect that easily occurs in traditional microporous molecular sieves.

[0022] 2. This invention introduces 1,4-bis(3-methylimidazolyl)butane dibromide, an ionic liquid. Compared with traditional ionic liquids, this ionic liquid contains two high-density imidazolium cation centers, which can form a more compact and stable supramolecular hydrogen bond network with the polar groups in the desulfurizing agent. This effectively blocks direct contact between oxygen in the air and the amine groups, inhibiting the oxidative degradation and discoloration of ethanolamines during long-term use. Simultaneously, its dual-cation structure firmly locks the active components within the system, reducing volatilization loss during high-temperature desorption, allowing the desulfurizing agent to maintain high activity even after multiple adsorption-desorption cycles.

[0023] 3. This invention utilizes the unique flexible butyl linkage structure in ionic liquids. During the adsorption stage, this structure helps maintain the stability of the system; while during the temperature-induced regeneration stage, the increased thermal motion of the flexible segments effectively disrupts the excessively rigid association between sulfur dioxide and the absorbent, reducing the high-temperature viscosity of the system. Combined with the mesoporous channels of the zirconium-modified aluminosilicate phosphate molecular sieve, this allows deeply adsorbed sulfur dioxide to escape rapidly and completely.

[0024] 4. In the preparation process, this invention uses ammonia water instead of strong alkali to adjust the pH value of the molecular sieve synthesis system to a slightly alkaline state (pH 7-7.5). This not only avoids the corrosion of the molecular sieve crystal framework caused by excessively high local alkalinity, but also effectively prevents the formation of inactive hydroxide precipitates from the zirconium source, ensuring that metallic zirconium can uniformly enter the molecular sieve framework. Furthermore, the entire preparation process is carried out in a closed system under mild reaction conditions, with no large-scale discharge of waste gas, wastewater, or solid waste. The final product is a homogeneous and transparent liquid with no solid waste residue, conforming to the development trend of green chemistry and possessing good prospects for industrial application. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The following boehmite was purchased from Yangzhou Zhongtianli New Material Co., Ltd., with an alumina content of 99.9%. The following silica sol was purchased from Dongguan Huihe Yongsheng Nanotechnology Co., Ltd., with a silica content of 30%.

[0027] Example 1: A preparation process for a composite desulfurizing agent for absorbing sulfur dioxide: 1. Preparation of zirconium-modified silica-alumina molecular sieves: Step (1): Add 10 parts by weight of boehmite, 25 parts by weight of 80% phosphoric acid solution, and 8 parts by weight of silica sol to the reaction vessel, stir and mix to form a gel.

[0028] Step (2): Add 35 parts by weight of 10 wt% zirconium oxychloride solution to the gel as a metal source, add 10 parts by weight of hexadecyltrimethylammonium bromide as a mesoporous directing agent, add 10 parts by weight of tetraethylammonium hydroxide as a microporous template agent, mix evenly, and add dropwise 20% ammonia solution to adjust the pH value to 7 to obtain a mixture.

[0029] Step (3): Transfer the mixture into the reactor and hydrothermally crystallize it at 200°C for 24 hours.

[0030] Step (4): The product is washed with deionized water until the filtrate is neutral, dried at 110°C for 10 h and calcined at 600°C for 5 h to obtain zirconium-modified silica-alumina molecular sieve.

[0031] 2. Preparation of 1,4-bis(3-methylimidazolyl)butane dibromide: Nine parts by weight of 1-methylimidazolium and 35 parts by weight of anhydrous ethanol were added to a reaction vessel equipped with a condenser and mixed thoroughly. Ten parts by weight of 1,4-dibromobutane were then added dropwise. The mixture was heated to 85°C and kept under reflux. The mixture was stirred for 20 hours. The product was cooled to room temperature, and ethyl acetate was added. The mixture was allowed to stand and separate into layers. The mixture was filtered, and the solid was washed five times with ethyl acetate and dried under vacuum to obtain 1,4-bis(3-methylimidazolyl)butane dibromosalt.

[0032] 3. Preparation of composite desulfurizing agent: S1. Premixing and Activation: Mix 40 parts by weight of ethanolamine, 4 parts by weight of sodium hydroxide, and 1 part by weight of 1,4-bis(3-methylimidazolyl)butane dibromide evenly, heat to 50°C, and stir until the sodium hydroxide is completely dissolved to form a uniform and transparent modified amine solution.

[0033] S2. Loading of zirconium-modified silica-alumina phosphate molecular sieve: 2 parts by weight of zirconium-modified silica-alumina phosphate molecular sieve are loaded into the catalyst basket of the reactor.

[0034] S3. Polymerization reaction: Seal the reactor, replace the air with nitrogen, raise the temperature to 150°C, control the pressure at 1MPa, and continuously pump in 50 parts by weight of ethylene oxide. After the pumping is completed, age at 110°C for 1 hour.

[0035] S4. Post-processing: After the reaction is completed, the reaction solution is cooled to 40°C and centrifuged and filtered to recover the zirconium-modified silicon aluminum phosphate molecular sieve. The filtrate is the composite desulfurizing agent.

[0036] Example 2: A preparation process for a composite desulfurizing agent for absorbing sulfur dioxide: 1. Preparation of zirconium-modified silica-alumina molecular sieves: Step (1): Add 10 parts by weight of boehmite, 20 parts by weight of 85% phosphoric acid solution, and 10 parts by weight of silica sol to the reaction vessel, stir and mix to form a gel.

[0037] Step (2): Add 50 parts by weight of 5 wt% zirconium oxychloride solution to the gel as a metal source, add 10 parts by weight of hexadecyltrimethylammonium bromide as a mesoporous directing agent, add 5 parts by weight of tetraethylammonium hydroxide as a microporous template agent, mix evenly, and add dropwise 25% ammonia solution to adjust the pH value to 7.5 to obtain a mixture.

[0038] Step (3): Transfer the mixture into the reactor and hydrothermally crystallize it at 180°C for 48 hours.

[0039] Step (4): The product is washed with deionized water until the filtrate is neutral, dried at 100°C for 12 hours and calcined at 500°C for 6 hours to obtain zirconium-modified silica-alumina molecular sieve.

[0040] 2. Preparation of 1,4-bis(3-methylimidazolyl)butane dibromide: 8.5 parts by weight of 1-methylimidazolium and 20 parts by weight of anhydrous ethanol were added to a reaction vessel equipped with a condenser and mixed thoroughly. 10 parts by weight of 1,4-dibromobutane were added dropwise, and the mixture was heated to 80°C and kept under reflux. The mixture was stirred for 20 hours. The product was cooled to room temperature, and ethyl acetate was added. The mixture was allowed to stand and separate into layers. The mixture was filtered, and the solid was washed five times with ethyl acetate and dried under vacuum to obtain 1,4-bis(3-methylimidazolyl)butane dibromosalt.

[0041] 3. Preparation of composite desulfurizing agent: S1. Premixing and Activation: Mix 20 parts by weight of ethanolamine, 5 parts by weight of sodium hydroxide, and 2 parts by weight of 1,4-bis(3-methylimidazolyl)butane dibromide evenly, heat to 60°C, and stir until the sodium hydroxide is completely dissolved to form a uniform and transparent modified amine solution.

[0042] S2. Loading of zirconium-modified silica-alumina phosphate molecular sieve: 1 part by weight of zirconium-modified silica-alumina phosphate molecular sieve is loaded into the catalyst basket of the reactor.

[0043] S3. Polymerization reaction: Seal the reactor, replace the air with nitrogen, raise the temperature to 130°C, control the pressure at 2MPa, and continuously pump in 40 parts by weight of ethylene oxide. After the pumping is completed, age at 120°C for 1 hour.

[0044] S4. Post-processing: After the reaction is completed, the reaction solution is cooled to 60°C and centrifuged and filtered to recover the zirconium-modified silicon aluminum phosphate molecular sieve. The filtrate is the composite desulfurizing agent.

[0045] Example 3: A preparation process for a composite desulfurizing agent for absorbing sulfur dioxide: 1. Preparation of zirconium-modified silica-alumina molecular sieves: Step (1): Add 10 parts by weight of boehmite, 20 parts by weight of 85% phosphoric acid solution, and 6 parts by weight of silica sol to the reaction vessel, stir and mix to form a gel.

[0046] Step (2): Add 20 parts by weight of 15 wt% zirconium oxychloride solution to the gel as a metal source, add 10 parts by weight of hexadecyltrimethylammonium bromide as a mesoporous directing agent, add 15 parts by weight of tetraethylammonium hydroxide as a microporous template agent, mix evenly, and add dropwise 15% ammonia solution to adjust the pH value to 7 to obtain a mixture.

[0047] Step (3): Transfer the mixture into the reactor and hydrothermally crystallize it at 180°C for 48 hours.

[0048] Step (4): The product is washed with deionized water until the filtrate is neutral, dried at 110°C for 8 hours and calcined at 600°C for 4 hours to obtain zirconium-modified silica-alumina molecular sieve.

[0049] 2. Preparation of 1,4-bis(3-methylimidazolyl)butane dibromide: 9.5 parts by weight of 1-methylimidazolium and 45 parts by weight of anhydrous ethanol were added to a reaction vessel equipped with a condenser and mixed thoroughly. 10 parts by weight of 1,4-dibromobutane were added dropwise, and the mixture was heated to 85°C and kept under reflux. The mixture was stirred for 24 hours. The product was cooled to room temperature, and ethyl acetate was added. The mixture was allowed to stand and separate into layers. The mixture was filtered, and the solid was washed five times with ethyl acetate and dried under vacuum to obtain 1,4-bis(3-methylimidazolyl)butane dibromosalt.

[0050] 3. Preparation of composite desulfurizing agent: S1. Premixing and Activation: Mix 50 parts by weight of ethanolamine, 2 parts by weight of sodium hydroxide, and 0.5 parts by weight of 1,4-bis(3-methylimidazolyl)butane dibromide evenly, heat to 60°C, and stir until the sodium hydroxide is completely dissolved to form a uniform and transparent modified amine solution.

[0051] S2. Loading of zirconium-modified silica-alumina phosphate molecular sieve: 3 parts by weight of zirconium-modified silica-alumina phosphate molecular sieve are loaded into the catalyst basket of the reactor.

[0052] S3. Polymerization reaction: Seal the reactor, replace the air with nitrogen, raise the temperature to 130°C, control the pressure at 0.5MPa, and continuously pump in 60 parts by weight of ethylene oxide. After the pumping is completed, age at 100°C for 2 hours.

[0053] S4. Post-processing: After the reaction is completed, the reaction solution is cooled to 40°C and centrifuged and filtered to recover the zirconium-modified silicon aluminum phosphate molecular sieve. The filtrate is the composite desulfurizing agent.

[0054] Comparative Example 1: Compared with Example 1, this comparative example does not add zirconium-modified silica-alumina molecular sieve when preparing the composite desulfurizer.

[0055] Comparative Example 2: Compared with Example 1, this comparative example does not add 1,4-bis(3-methylimidazolyl)butane dibromide when preparing the composite desulfurizer.

[0056] Comparative Example 3: Compared with Example 1, this comparative example does not add zirconium oxychloride solution when preparing zirconium-modified silica-alumina phosphate molecular sieve.

[0057] 1. Preparation of zirconium-modified silica-alumina molecular sieves: Step (2): Add 10 parts by weight of hexadecyltrimethylammonium bromide as a mesoporous guiding agent and 10 parts by weight of tetraethylammonium hydroxide as a microporous template agent to the gel, mix evenly, and add dropwise a 20% ammonia solution to adjust the pH value to 7 to obtain a mixture.

[0058] The other steps are the same as in Example 1.

[0059] Comparative Example 4: Compared with Example 1, this comparative example does not add hexadecyltrimethylammonium bromide when preparing zirconium-modified silica-alumina molecular sieve.

[0060] 1. Preparation of zirconium-modified silica-alumina molecular sieves: Step (2): Add 35 parts by weight of 10 wt% zirconium oxychloride solution to the gel as a metal source, add 10 parts by weight of tetraethylammonium hydroxide as a micropore template agent, mix evenly, and add dropwise 20% ammonia solution to adjust the pH value to 7 to obtain a mixture.

[0061] The other steps are the same as in Example 1.

[0062] The composite desulfurizers prepared in Examples 1-3 and Comparative Examples 1-4 were evaluated by adsorption and regeneration using an intelligent constant temperature bubbling absorption device.

[0063] 100g of composite desulfurizing agent was loaded into a bubbling absorption bottle equipped with a sand core aerator. The absorption bottle was placed in a constant temperature water bath, with the water bath temperature controlled at 40℃ (simulating industrial absorption temperature), and operated at atmospheric pressure. The total gas flow rate was controlled at 3L / min. When the sulfur dioxide concentration in the outlet gas exceeded 50mg / m³, absorption was considered saturated, the gas flow was stopped, the breakthrough time was recorded, and the saturated sulfur capacity was calculated. The saturated desulfurizing agent was heated to 120℃, and nitrogen gas was introduced for desorption and regeneration until no liquid flowed out of the condenser and no sulfur dioxide was detected in the outlet gas. After cooling to room temperature, the next round of absorption experiments was conducted.

[0064] The composition of sulfides in the outlet gas of the bubble absorption bottle was determined by gas chromatography equipped with an FPD detector (flame photometric detector). Simultaneously, the sulfur dioxide content in the feed gas was analyzed according to SY / T6537-2002 "Analytical Methods for Gases and Solutions in Natural Gas Purification Plants".

[0065] The raw gas comprises the following components in molar fractions: 1% sulfur dioxide, 3% oxygen, 25% carbon dioxide, and the balance being nitrogen.

[0066] Desulfurization efficiency (K) calculation: In the formula, C1 is the volume fraction (%) of sulfur dioxide in the inlet gas; C2 is the volume fraction (%) of sulfur dioxide in the outlet gas.

[0067] Calculation of saturated sulfur capacity (Q): In the formula, F is the gas flow rate (L / min); C vol t is the volume ratio of sulfur dioxide in the inlet gas (i.e., 0.01); t is the breakthrough time (min); M is the molar mass of sulfur dioxide (64 g / mol); m is the mass of desulfurizing agent (g).

[0068] Table 1. Desulfurization efficiency of composite desulfurizing agents

[0069] As shown in Table 1, the composite desulfurizers prepared in Examples 1-3 are superior to the comparative examples in terms of breakthrough time, saturated sulfur capacity, and cycle stability. The zirconium-modified silica-alumina molecular sieve used in Examples 1-3, by introducing zirconium, enhances its catalytic activity and selectivity for the ring-opening polymerization of ethanolamine and ethylene oxide. Simultaneously, the dual-template system composed of hexadecyltrimethylammonium bromide and tetraethylammonium hydroxide constructs a multi-level pore structure with mesoporous and microporous coexistence in situ. This unique pore system optimizes the mass transfer and diffusion pathways between reactants and products, thereby improving absorption kinetics, directly manifested as a longer breakthrough time and higher saturated sulfur capacity.

[0070] The 1,4-bis(3-methylimidazolyl)butane dibromide added in Examples 1-3 has a dual cationic center and a flexible alkyl chain structure. Its dual cationic center can interact electrostatically with the anionic sites in the polymerization product to form a denser and more stable three-dimensional ionic network, which effectively inhibits the loss and structural degradation of the active component in repeated adsorption-desorption cycles. Its flexible chain structure helps to reduce the viscosity of the system during regeneration and promotes the desorption and diffusion of sulfur dioxide, thereby achieving a high regeneration efficiency.

[0071] Compared with Example 1, Comparative Example 1 did not add zirconium-modified silica-alumina molecular sieve when preparing the composite desulfurizer. Due to the lack of zirconium-modified silica-alumina molecular sieve catalyst, the polymerization reaction of ethanolamine and ethylene oxide was in a disordered and uncontrollable state, the molecular weight distribution of the product was too wide and there were many by-products, resulting in the lowest sulfur capacity, the slowest absorption and poor cycle stability.

[0072] Compared with Example 1, Comparative Example 2 did not add 1,4-bis(3-methylimidazolyl)butane dibromide when preparing the composite desulfurizer. Due to the lack of electrostatic crosslinking and mass transfer promoting function of bisimidazolium salt, the three-dimensional network of the product was loose, which led to the loss of active components during regeneration, thus deteriorating the cycle stability.

[0073] Compared with Example 1, Comparative Example 3 did not add zirconium oxychloride solution when preparing zirconium-modified silica-alumina molecular sieve. Without zirconium to provide acidic sites, the catalytic activity and selectivity were insufficient, and the structure of the generated desulfurizer was poor, resulting in low sulfur capacity, absorption rate and regeneration efficiency.

[0074] Comparative Example 4: Compared with Example 1, this comparative example did not add hexadecyltrimethylammonium bromide when preparing zirconium-modified silica-alumina molecular sieve. Due to the lack of mesoporous structure and the existence of only micropores, the mass transfer and diffusion efficiency between reactants and products was limited, resulting in a shortened breakthrough time and slower absorption kinetics.

[0075] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A composite desulfurizer for absorbing sulfur dioxide, characterized by comprising a porous carrier and a sulfur compound adsorbing agent supported on the carrier, wherein the sulfur compound adsorbing agent is a compound of a transition metal element and sulfur. The composite desulfurizing agent for absorbing sulfur dioxide is prepared by reacting the following raw materials: 20-50 parts by weight of ethanolamine, 40-60 parts by weight of ethylene oxide, 2-5 parts by weight of sodium hydroxide, 1-3 parts by weight of zirconium-modified silica-alumina molecular sieve, and 0.5-2 parts by weight of 1,4-bis(3-methylimidazolyl)butane dibromide.

2. The composite desulfurizer for absorbing sulfur dioxide according to claim 1, characterized by, The preparation method of the zirconium-modified silica-alumina molecular sieve is as follows: Step (1): Add boehmite, 80-85% phosphoric acid solution, and silica sol to the reaction vessel, stir and mix to form a gel; Step (2): Add zirconium oxychloride solution as a metal source, hexadecyltrimethylammonium bromide as a mesoporous directing agent, and tetraethylammonium hydroxide as a microporous template agent to the gel. Mix well and add 15-25% ammonia solution to adjust the pH to 7-7.5 to obtain a mixture. Step (3): Transfer the mixture into a reactor and hydrothermally crystallize it at 180-200℃ for 24-48 hours; Step (4): The product is washed with deionized water until the filtrate is neutral, dried at 100-110℃ for 8-12h and calcined at 500-600℃ for 4-6h to obtain zirconium-modified silica-alumina molecular sieve.

3. The composite desulfurizer for absorbing sulfur dioxide according to claim 2, characterized by, In step (1), the mass ratio of boehmite, phosphoric acid solution with a concentration of 80-85%, and silica sol is 1:(2-2.5):(0.6-1).

4. The composite desulfurizing agent for absorbing sulfur dioxide according to claim 2, characterized in that, In step (2), the concentration of the zirconium oxychloride solution is 5-15 wt%.

5. The composite desulfurizing agent for absorbing sulfur dioxide according to claim 2, characterized in that, In step (2), the mass ratio of zirconium oxychloride solution to hexadecyltrimethylammonium bromide is (2-5):1; and the mass ratio of tetraethylammonium hydroxide to boehmite is (0.5-1.5):

1.

6. The composite desulfurizing agent for absorbing sulfur dioxide according to claim 1, characterized in that, The preparation method of the 1,4-bis(3-methylimidazolyl)butane dibromide is as follows: 1-Methylimidazole and anhydrous ethanol were added to a reaction vessel equipped with a condenser and mixed thoroughly. 1,4-Dibromobutane was added dropwise, and the mixture was heated to 80-85°C and kept under reflux. The mixture was stirred for 20-24 hours. The product was cooled to room temperature, and ethyl acetate was added. The mixture was allowed to stand and separate into layers. The mixture was filtered, and the solid was washed five times with ethyl acetate and dried under vacuum to obtain 1,4-bis(3-methylimidazolyl)butane dibromosalt.

7. The composite desulfurizing agent for absorbing sulfur dioxide according to claim 6, characterized in that, The mass ratio of 1-methylimidazole, anhydrous ethanol, and 1,4-dibromobutane is (8.5-9.5):(35-45):

10.

8. The composite desulfurizing agent for absorbing sulfur dioxide according to claim 1, characterized in that, The preparation process of the composite desulfurizing agent for absorbing sulfur dioxide is as follows: S1. Premixing and activation: Mix ethanolamine, sodium hydroxide, and 1,4-bis(3-methylimidazolyl)butane dibromide evenly, heat to 50-60℃, and stir until sodium hydroxide is completely dissolved to form a uniform and transparent modified amine solution. S2. Loading of zirconium-modified silica-alumina phosphate molecular sieve: The zirconium-modified silica-alumina phosphate molecular sieve is loaded into the catalyst basket of the reactor; S3. Polymerization reaction: Seal the reactor, replace the air with nitrogen, raise the temperature to 130-150℃, control the pressure at 0.5-2MPa, continuously pump in ethylene oxide, and after the pumping is completed, age at 100-120℃ for 1-2 hours. S4. Post-processing: After the reaction is completed, the reaction solution is cooled to 40-60℃ and centrifuged and filtered to recover the zirconium-modified silicon aluminum phosphate molecular sieve. The filtrate is the composite desulfurizing agent.

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